documentation licenses

Since it seems rather unclear whether or not the GFDL and OPL
are DFSG-free with all permutations of their optional clauses,
is anyone suggesting that documentation in Debian be held
to a different standard than the DFSG?
On the other hand, if the various restrictions on modification
and printed copies in the GFDL can be considered DFSG-free,
then what about such restrictions in the OPL?
Would it be possible for a document to be licensed "freely" yet
prevent commercial printed copies to go into main under current
or future guidelines?
If there are to be separate standards for documentation, how
would such documentation qualify, and how can the potential
slippery slope be avoided?